Worm forming apparatus



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Feb. 3, 1959 5. E. SAARI 2,871,765

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" WORM FoRMING APPARATUS Filed oct. e, 1955 4 sheets-sheet 4 United States Patent C WORM FORMING APPARATUS Oliver E. Saarl, Schler Park, Ill., assignor to Illinois Tool Works, Chicago, Ill., a corporation of Illinois Application October 6, 1955, Serial N o. 538,823

3 Claims. (Cl. 90-11.64)

The present invention relates to a novel method and apparatus for forming helical threads or the like on a workpiece, and more particularly to a novel method and apparatus for forming, as by milling .or grinding, helical threads having substantially constant tapered leads.

Heretofore, when forming threads of constant tapered leads, it has been the general practice to maintain a constant angular relationship between the work and the cutting or forming tool. This causes the shape of the thread prole to vary along the thread as a result of the actual changing lead angle of the thread being formed, which lead angle increase as the diameter of the thread decreases. Such a changing thread profile has several disadvantages and is especially undesirable for threads of worms of the type disclosed in my Patent No. 2,696,- 125, led July 12, 1954.

An important object of the present invention is to provide a novel method and apparatus for forming helical threads or the like having constant tapered leads in a manner so as to provide such threads with substantially constant proles.

A more specific object of the present invention is to provide a novel apparatus for forming threads of constant tapered leads wherein the lead angle setting between a forming tool and the work may be continually changed in timed relationship to relative axial or lead motion of a workpiece so that the resulting threads will be provided with substantially constant profiles.

Further objects of the present'invention are to pro vide a novel apparatus of the above described type which is simple in construction and operation and which may be constructed in the form of a relatively economical attachment adapted to be mounted on a standard thread milling machine or the like.

Other objects and advantages of the present invention will become apparent from the following description and the accompanying drawings wherein:

Fig. 1 is a fragmentary sectional view taken along line 11 in Fig. 2;

Fig. 2 is a fragmentary sectional view taken along line 2-2 in Fig. 1;

Fig. 3 is a fragmentary plan view of an apparatus embodying the principles of the present invention;

Fig. 4 is a fragmentary sectional view taken along line 4-4 in Fig. 3;

Fig. 5 is an enlarged fragmentary sectional view taken along line 5-5 in Fig. 3;

Fig. 6 is a fragmentary sectional view taken along line 6 6' in Fig. 3;

Fig. 7 is a fragmentary sectional view taken along line 7*7 in Fig. 3; and

Fig. 8 is a simplified elevational view showing how the grinding wheel or cutting tool may be tilted relative to the axis of the workpiece.

Referring now more specifically to the drawings wherein like parts are designated by the same numerals throughout the various figures, an apparatus 10 shown for the rice purpose of illustrating the present invention includes a base 12 having head and tail stock 14 and 16 of known construction mounted thereon respectively providing centers 18 and 20 for supporting a workpiece 22. The workpiece 22 which is shown for illustrative purposes includes a tapered worm section 24 having threads v26 of constant tapered leads tobe formed. A forming tool 28 which may be a grinding wheel as shown or a milling cutter or the like is provided for forming the threads 26 in the manner described below.

In Figs. l through 5 the grinding wheel is shown mounted for rotation about an axis parallel to the axis of the workpiece in order to facilitate illustration of the apparatus, but in accordance with the present invention, the grinding wheel is mounted so that its axis of rotation may be disposed at an angle to the axis of the workpiece as shown in Fig. 8 during grinding of a tapered helical thread or the like. In addition, the grinding wheel or cutting tool mounting means is constructed so that the angle between the axis of the grinding wheel and the work may be constantly varied in a predetermined manner as the work and grinding wheel are relatively fed axially of each other. In order to accomplish this the grinding wheel is carried by a bracket 30 which is pivotally mounted on carriage or slide means 32 shiftable transversely with respect to the work and, in turn, slidably disposed on carriage or slide means 34 shiftable axially with respect to the work.

The slide or carriage means 34 comprises a platelike member 36 disposed on longitudinally extendingl guideways of the machine base 12, and a transversely extending guide member 38 having a dovetail guide 40 thereon. The carriage means 34 is fed axially of the work by means of a feed screw 42 cooperating with a depending nut member 44 fixed to the slide plate 36'. Means described below is provided for driving the feed screw 42.

The slide or carriage means 32 comprises a slide block 46 having a dovetail slot therein receiving the dovetail guide 40 of the guide member 38. In order to feed the carriage means 32 and thus the cutting tool or grinding wheel transversely with respect to the workpiece, the slide block 46' is operatively connected with a lixed cam member 48 which serves to shift the slide block along the guide member 38 as the carriage means 34 is fed generally axially of the workpiece. More specifically, a screw rod 50 is provided which extends through a bore in the guide member 38 and has its inner end threaded into a nut member 52 depending from the slide block 46. The outer end of the rod S0 extends through a tting 54 secured to the end of the guide member 38 by a plurality of screws or the like 56. As shown in Figs. 2, 3 and 4, a sleeve member 58 is slidably disposed within the fitting 54 and rotatably receives an outer end portion of the rod 50. A collar or flange 60 is disposed on the rod 50 and is slidable in a counterbore 62 formed in the guide member 38, and a spacer or extension 64l ber 58 from rotating, a slot 68 is formed therein, and a cover plate 70 is secured to the litting 54 and has a depending key portion 72 extending into the slot. A pointer 74 is provided for cooperating with a scale 76 on the handle member 66 for indicating the position to which the transverse carriage means is adjusted, and the pointer," ,member has a base portion 78y dispos'edin the slot 68;

Patented Feb. 3, 1959,l

germes and secured to the sleeve member 58 by means of screws 80.

A block 82 is secured to the under side of the sleeve member 58 by a plurality of screws 84, which block rigidly carries a pin 86. The pin 86 extends snugly into a cam follower block 88 Vslidably disposed in a cam slot 90 formed in the cam member 48. As shown best in Fig. 3, the cam slot 90 is disposed at an angle to the axis of the workpiece, which angle is equal to the taper angle of the workpiece. Thus, as the carriage means and cutting tool are fed generally axially of the workpiece, the cam follower block S8 slides along the slot 90 and shifts the sleeve member 58, which sleeve member, in turn, shifts the rod 50 and the transverse carriage means 32. As a result, the cutting tool or grinding wheel is simultaneouslyfed axially of and transversely of the workpiece along a diagonal path of travel parallel with the tapered surface of the workpiece.

The cam member 48 is mounted on a bar 92 which in turn, is supported on the main frame 12 by a pair of brackets 94, only one of which is shown. A plurality of set screws 96 is provided for adjustably fixing the cam member 4S on the bar 92. In the embodiment illustrated, the fitting member54 is provided with a downwardly facing slot 93 slidably receiving the cam member so as to insure proper lateral spacing of the cam member with respect to the transverse carriage means, and a bottom cover plate 100 may be secured to the bottom of the fitting by means of screws or the like, if desired.

As shown in Figs. 1, 2, 3 and 5, the transverse carriage means comprises a bearing block 102 mounted on the slide member 46 and rotatably supporting a shaft 104. The Shaft 104 is retained against axial movement relative to the bearing block 102 by thrust bearing means which includes a pair of spaced rings 1.06 and S separated from each other by a spacer ring 110 and fixed to one end of the bearing block 102 by a plurality of screws 112. A thrust bearing flange 114 is secured to the end of the shaft 104 by a plurality of screws 116 and extends between the rings 106 and 103 as shown best in Fig. 5.

The above mentioned bracket has a sleeve portion 118 surrounding the shaft 104 and retained against axial movement by a pair of collars 120 and 122 fixed on the shaft by set screws 124 and 126. The bracket 30 also includes a platform portion 12S on which there is mounted an electric motor 130 for driving tbe cutting tool or grinding wheel, and a laterally extending arm portion 132. A hollow block 134 is secured to the arm portion by a plurality of screws 136 and receives a tubular sleeve member 13S which rotatably supports a shaft 140. The grinding wheel 2S or cutting tool is fixed on the shaft 140 in any suitable manner. Pulleys 142 and 144 are respectively mounted on the motor shaft and the shaft 140, and an endless belt 146 extends around these pulleys to provide a driving connection between the motor and the tool shaft 140.

It should be noted that the axis of the shaft 104 or in other words, the axis of pivotal movement of the bracket 30 intersects and is perpendicular to the axis of rotation of the workpiece and that the rotative axis of the grinding wheel 28 or cutting tool intersects and is perpendicu- `lar to the axis of the shaft 104. Furthermore, the bracket 30 and related elements for supporting the grinding wheel are formed to locate the grinding wheel 23 so that it intersects and is bisected by the axis of the shaft 104. Thus, when the grinding wheel is tilted relative to the work in the manner described below, it will be pivoted` about a point on the axis of the shaft 104 whereby the point of contact between the grinding wheel and the workpiece will always be substantially in a plane including the rotative axis of the work and the rotative axis of the shaft 104. Therefore, the grinding wheel may be set to form the workpiece threadl by inclining ythe rotative axis of the grinding wheel at an.'V angle to the-rotative axis of the work which is substantially equal to the desired lead angle of the thread to be formed.

In order to adjust initially the bracket 30 and, therefore, the rotative axis of the grinding wheel to the desired angle with respect to the rotative axis of the work, a worm 143 is provided on a shaft 150 for meshing with teeth of a worm gear section 152 on the shaft 104. The shaft is journalled in bushings 154 and 156 mounted in the bracket 30, which bushings also retain the worm 148 against axial movement. r1`he bushing 154 is fixed with respect to the bracket 30 by one or more screws 158. An outwardly projecting end portion of the shaft 150 is formed to receive a suitable tool, not shown, whereby the shaft 150 may be rotated to pivotally or rotatively adiust the bracket 30 relative to the shaft 104. The bracket 30 is releasably locked in the desired adjusted position relative to the shaft 104 by the means shown best in Figs. 5 and 6. More specifically, a bore 162 is formed in the bracket 30, which bore is intersected by the shaft 104. A bushing 164 is disposed in the bore for providing a bearing for a shaft 166 which has an inner threaded end cooperating with an internally threaded wedge block 16S. A handle member 170 is connected with the outer end of the shaft 166 so that by turning the handle member the block 160 may be drawn toward and wedged against the shaft 104 to lock the shaft and bracket member 30 against relative rotation.

in order constantly to vary the angular relationship between the rotative axes of the workpiece and the grinding wheel shown in Fig. S as the grinding wheel is fed along the workpiece, means is provided for pivoting the shaft 104 in predetermined timed relationship with the feed motion of the grinding wheel. More specifically, a feed screw or worm 172 is journalled in the bearing block 102. as shown in Figs. 1, 3 and 5 for meshing with teeth of a worm gear section 174 formed in the shaft 102. The shaft of the worm 172 is connected with a universal joint 174 which, in turn, is connected with a drive shaft 176. One end of the drive shaft 176 is supported by a bearing 178 mounted on the slide block 36 of the slide or carriage means 34 and the opposite end of the shaft 176 is connected with a change gear assembly 180. Power for the apparatus is supplied through a drive shaft 182 from any suitable source, not shown, and the feed screw 42 and the drive shaft 176 are driven from the main drive Shaft 102 in predetermined timed relationship through the gears of the change gear assembly 180. The change gear assembly may be of any known construction and, therefore, need not be described in detail. It suffices to state that by using the proper change gear ratio, the worm 172 may be driven to cause the grinding wheel angle setting to follow closely the changing lead angle of any tapered helix as the grinding wheel is fed along the workpiece. As set forth hereinabove, this results in the provision of a tapered helical thread or the like which has a substantially uniform profile.

lt will be noted that rotation is imparted to the workpiece 22 by coupling said workpiece with the live center 18 by a suitable dog 18a, Fig. 3. The center 13 is driven through conventional driving mechanism not shown so as to impart rotation to the work in timed relation with the movement of parts heretofore described.

When the metal working or forming tool is a grinding wheel as shown, a truing device may be mounted on the apparatus for maintaining the desired shape of the grinding wheel. Such a truing device may include bracket means mounted ou the bearing block 102. Tool holders 194 and 196 are adjustably mounted on the bracket means for locating tools 198 and 200 for engaging a peripheral portion of the grinding wheel.

From the above description it is seen that the present invention has provided a novel method and apparatus whereby helical threads or the like of constant tapered lead may be easily and automatically formed so as to have substantially uniform profiles. More specifically,

it is seen that the present invention has provided a novel method and apparatus whereby such threads or the like may be formed by constantly changing the relative angular relationship between the axis of the workpiece and rotatable metal working tool in accordance with the changing lead angle of the thread being formed as the tool is fed relatively along the workpiece. One advantage of the method and apparatus of the present invention is that a relatively large diameter rotary cutting tool or grinding wheel may be used as compared with the size of a grinding wheel which may be used when the angular setting of the grinding wheel is xed, and as a result, more rapid and economical production of the workpiece is promoted. Furthermore, threads of the type contemplated herein having substantially uniform proles may 'be more easily matched with the teeth of a member provided for meshing with the workpiece.

While the preferred embodiments of the present invention have been shown and described herein, it is obvious that many structural details may be changed without departing from the spirit and scope of the appended claims.

The invention is claimed as follows:

1. An apparatus for machining a helical tapered thread or the like having a changing lead angle on a workpiece, comprising base means, means on said base means for rotatably supporting a workpiece for rotation about a predetermined axis, a rst carriage means disposed on said base means for movement generally longitudinally of said predetermined axis, second carriage means shiftably disposed on said first mentioned carriage means for movement transversely of said predetermined axis, a rotatable shaft mounted on said second carriage means for pivotal movement about an axis intersecting and substantially perpendicular to said first mentioned axis, support means fixed on said shaft carrying rotatable means for supporting a rotatable tool for rotation about a third axis intersecting and substantially perpendicular to said second mentioned axis, a tool when disposed on said rotatable means being substantially bisected by said second mentioned axis, means mounted on said last mentioned support means for driving said rotatable means, means on said base means for simultaneously feeding said rst and second carriage means to move a tool on said rotatable means diagonally with respect to said first mentioned axis, and means on said base means for pivoting said shaft in timed relationship with said diagonal feeding movement for positioning said third mentioned axis at changing angles with respect to said first mentioned axis in accordance with the changing lead angle of the thread.

2. An attachment adapted to be mounted on a thread milling machine or the like for machining a helical tapered thread or the like having a changing lead angle, comprising a first carriage means movable generally longitudinally of a workpiece to be machined, a second carriage means disposed on said first carriage means and movable transversely of said `lrst carriage means, means connected with said first carriage means for actuating said first carriage means, fixed cam means operatively interconnected with said second carriage means for actuating said second carriage means upon movement of the first carriage means, shaft means mounted on said second carriage means for pivotal movement about a predetermined axis, means carried by said pivotally mounted shaft means for rotatably supporting a tool in position to be intersected and substantially bisected by said predetermined axis and for rotation about an axis intersecting and substantially perpendicular to said predetermined axis, and means connected with said pivotally mounted shaft means for actuating said pivotally mounted means in predetermined timed relationship with said first mentioned actuating means.

3. Apparatus for machining a helical thread or the like having a changing lead angle on a conical workpiece, and comprising base means, means on said base means for supporting a workpiece for rotation about a predetermined axis, a shaft mounted on said base means for rotation about an axis intersecting said predetermined axis and in a plane 'containing the said predetermined axis, means fixed on and movable with said shaft for supporting a rotatable tool for rotation about a third axis disposed at an angle with respect to said predetermined axis so that the periphery of said tool is disposed at the proper lead angle, means on said base means for relatively feeding the workpiece supporting means and said shaft generally axially and transversely of said predetermined axis for creating a traverse of the tool with relation to a workpiece and determining the thread lead, and means on said base means acting simultaneously therewith for relatively pivoting said shaft about said second axis for changing the angle between said predetermined axis and said third-mentioned axis to change the periphery of said tool in accordance with the changing lead angle of the thread to be produced as the tool and workpiece are moved relatively axially with respect to said workpiece.

References Cited in the tile of this patent UNITED STATES PATENTS 607,626 Reece .Tuly 19, 1898 627,299 Echols June 20, 1899 1,340,031 Fitzpatrick May 11, 1920 1,376,155 Muller Apr. 26, 1921 1,960,460 Shurr May .29, 1934 2,392,752 Marsilius Jan. 8, 1946 2,405,485 Barstrom et al. Aug. 6, 1946 

